Atoms, elements and compounds - AQAChemical formulae of ions
Chemists use symbols and formulae to represent elements and compounds. Word equations and balanced chemical equations represent the changes that happen in chemical reactions.
An ionElectrically charged particle, formed when an atom or molecule gains or loses electrons. is a charged particle formed when an atomThe smallest part of an element that can exist., or a group of atoms, loses or gains electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. The number and sign of its electrical charges are shown in superscriptA character (number, letter or symbol) that appears slightly above the normal line of type, and that is usually smaller than the rest of the text. text.
Names and formulae of some common ions:
Name of ion
Formula of ion
Electrical charge(s)
Sodium
Na+
One positive
Magnesium
Mg2+
Two positive
Chloride
Cl-
One negative
Oxide
O2-
Two negative
Name of ion
Sodium
Formula of ion
Na+
Electrical charge(s)
One positive
Name of ion
Magnesium
Formula of ion
Mg2+
Electrical charge(s)
Two positive
Name of ion
Chloride
Formula of ion
Cl-
Electrical charge(s)
One negative
Name of ion
Oxide
Formula of ion
O2-
Electrical charge(s)
Two negative
Simple formulae
The formula of an ionic compoundAn ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). can be predicted using the formulae of its ions. The numbers of ions in a formula must give an equal number of positive and negative charges.